The demand for improved screenings treatment systems to process screenings from waste water continues to increase, with the demand being greatest for screenings treatment systems that are compact, that have low installation and maintenance costs, and that process screenings to produce a clean, odorless discharge with a significantly reduced volume for lower transport and landfill costs.
One such screenings treatment system developed by JWC ENVIRONMENTAL is the SCREENINGS WASHER SYSTEM. This system includes a hopper, a grinder disposed beneath the hopper, and an inclined wash system beginning below the grinder and extending upwards beyond the hopper. The wash system includes an inclined auger rotor, a spray wash system, and an inclined screen that are housed in a straight discharge tubular structure. In operation, the hopper receives screenings captured by a bar screen and gravity feeds the screenings to the grinder for solids reduction. The ground screenings are then gravity fed to the wash system. Softer organics (such as fecal material) and wash fluid from the spray wash system pass through openings in the inclined screen. The unwanted solids are captured and transported upwards by the auger to the discharge end of the tubular structure for disposal. The soft organics and the wash fluid are returned to the plant's waste stream.
Since the SCREENINGS WASHER SYSTEM is a “pull” type system that uses an inclined auger to wash and transport the screenings, the discharged screenings are fragmented, and, therefore, take up considerable space compared to compacted screenings that are formed into plugs. Furthermore, the inclined washer results in a system that requires a relatively large space.
WO 93/02800 discloses a screenings treatment system that includes a hopper, a coarse material separator disposed in the hopper, a mechanical reduction unit disposed below the hopper, a mixing trough with a horizontal mixer and a wash fluid sprayer disposed below the mechanical reduction unit, a de-watering and compaction unit adjacent the mixing trough, and a discharge pipe coupled to a discharge end of the de-watering and compaction unit.
In operation, the hopper receives screenings onto the coarse material separator, which removes coarse material. The remaining screenings are fed into the mechanical reduction unit, which shears the screenings. The sheared screenings are received by the mixing trough overflowing with water sprayed from wash fluid sprayer. The horizontal mixer swirls the water and the screenings to wash the screenings and dissolve the soluble matter contained therein. The dissolved soluble matter and screenings near the top of the mixing trough are carried by the overflowing water over an overflow edge of the mixing trough and into the de-watering and compaction unit. The de-watering and compaction unit includes a conveyor and de-watering screw arranged inside a screen housing that discharges liquid into a drain. The conveyor and de-watering screw transports the washed screenings that remain in the screen housing to an axial end of the screen housing. There, the end of the conveyor and the de-watering screw projects into the discharge pipe. The discharge pipe is curved upwards and rises up to an elbow whose discharge end is located above a container for final disposal. The screenings transported into the discharge pipe form a friction plug in the pipe. This causes the screenings to be compacted and simultaneously de-watered.
One disadvantage with the screenings washer system disclosed in WO 93/02800 is the provision of the mixing trough with its own horizontal mixer and wash fluid sprayer and the separate de-watering and compaction unit adjacent the mixing trough. This complicates the system significantly, requiring an additional motor to operate the horizontal mixer. In addition, the mixing trough operates on the principle that the screenings will overflow from the top edge of the trough. However, in reality, screenings may collect at the bottom of the mixing trough. Furthermore, since the fluid sprayer sprays into the mixing trough and not onto the screw and screen housing, the screw and screen housing are not continuously washed with clean water, thereby adding to the maintenance costs.
This invention is directed to an improved screenings washer that overcomes one or more of the problems set forth above.